1. Field of the Invention
The invention relates generally to the field of network services. More particularly, the present invention relates to a technique for locating a point of ingress, or injection point, of a foreign, or unwanted, signal in a network. Further, by locating a point of ingress, or injection point, of a foreign signal in a network, a site of potential egress, or signal leakage, is located.
2. Background of the Art
In the field of network services, there is much concern about both ingress of foreign signals and egress of transmission signals. Egress, or signal leakage, must be monitored and kept to a minimum to avoid interference with atmospheric signals using the same frequencies. Ingress, or interference, involves an outside signal coupled to an actual signal in the network, distorting the actual signal being transmitted. Ingress and egress can represent major costs to network operators and it is necessary to be able to locate and correct the ingress/egress point in the network in order to provide quality network communication.
For example, in networks including Very high-rate Digital Subscriber Lines (VDSL) operating on twisted pair networks, interference may occur when energy from another service, such as, for example, T1 or ADSL or FCC licensed services, appears as in-band energy to the victim line. Interference may also result from distortion caused by non-linearities within a home translating energy from out-of-band signals into the VDSL band. In cable TV networks, impairments in the network such as flaws in cable joints and connections, cracks, and loose cable shields serve as points of ingress and egress.
Locating the point of ingress/egress, however, is not an easy task. Very often, the signals themselves are noise-like in nature, covering many MHz of bandwidth, and thus causing difficulty in identifying the signals. One scheme suggested to assist with signal identification is the use of a distinctive signature. This suggestion, however, poses a significant disadvantage, as only part of the signal strength available in the original signal is provided by the signal bearing the distinctive signature. In addition, data-carrying capacity may be diminished if the signature is in the signaling band.
In the case of cable TV networks, ingress and egress have conventionally been measured using field strength meters tuned to specific channels, as allocated by the FCC, for monitoring. These meters are typically not extremely sensitive or reliable, being limited in their detector bandwidth to several kHz. Many of these meters also do not permit discrimination between different foreign signals and injection points in a network. In order to discriminate, some meter systems modulate the signal in a cable with a tag, which is then demodulated and used to identify the leakage. Furthermore, the use of these systems is often time-consuming. An alternative practice is to measure ingress to a network and then selectively and systematically remove segments of the network until the ingress is eliminated. This procedure necessarily involves undesirable disruption of communication over the network.
It should be understood that any point where ingress occurs is a potential point of egress, and vice versa. Because it is frequently an easier task to identify ingress into a system, the testing for egress may be prompted by monitoring ingress. Locating the source of ingress/egress often involves testing and locating the point of egress of a signal carried by the transmission cable. In locating this point, an ingress point has also been located.
Further, it should be understood that a method and system for estimating a location of an injection point of foreign signals in a network is not limited to use with VDSL or cable TV networks, but is instead applicable to communication networks in general. As noted above, in determining an injection point of foreign signals, it is understood that a potential egress site has also been located.
Accordingly, there is presently a need for a technique to locate the injection point of a foreign signal in a network that is sufficiently sensitive and reliable, yet is not overly time consuming and further, does not cause unnecessary disruption of communication over the network. There is also a need for a technique that has the capability to locate multiple points of ingress. Further, it is also desirable to have a technique that permits monitoring of a network so that impairments can be identified, measured, and tracked before a communication disruption occurs.